Equipment/general tips for casting/uploading let's play videos

Hi, I'm SusaVile. I wanted to ask what microphone does Day9 use, as well as how does he manage to get good quality audio (and audio levels) throughout the cast. I'm starting some "let's play" videos on youtube, and I wanted to improve the quality of my commentary as well as the general audio issues. Any tips are welcome, but I would still like to know which microphone and additional gear that Day9 uses, as I would be quite happy with that quality. Feel free to give me any additional tips, as I'm starting but already uploading some videos. Thank you. Edit: here's the channel link to youtube, I'm starting with medieval total war but will definitely cast some HOTS games and other gaming stuff as I get more confortable. http://www.youtube.com/user/Jahander23